1. Field of the Invention
This invention relates to a method of driving a liquid crystal display, and more particularly to a method of driving a liquid crystal display that is adaptive for displaying pixel color with increased brightness in a liquid crystal cell.
2. Description of the Related Art
Generally, an active matrix liquid crystal display (LCD) uses a thin film transistor (TFT) as a switching device to display a moving picture. Since the LCD is able to provide a product having a smaller dimension than a Brown tube or cathode Ray Tube, it has been widely used in various applications of personal computers, notebook computers, office automation equipment such copy machines, etc., and portable equipment such as a cellular phones, pagers, etc.
A liquid crystal display device includes a liquid crystal layer capable of rotating the polarizing direction of light by applying an electric field. Such LCD device includes a common electrode, which is a transparent conduction film formed on an entire glass substrate for applying a voltage to the liquid crystal layer; a thin film transistor (TFT), substrate electrodes composed of a plurality of pixel electrodes; and a plurality of TFTs connected to one another. The liquid crystal display device further includes each TFT device in which each transistor resides between a gate line and a signal line of a TFT substrate and is connected to a gate pad and a data pad to control a voltage for controlling the polarizing characteristics of light passing the liquid crystal layer; a light source; and an optical system making the light incident to the TFT substrate uniform in direction; a straight polarizer which resides between the light source and the TFT substrate; an analyzer attached to the common electrode substrate; and various color filters which are combined with each pixel electrode between a polarizer and a pixel electrode to display one basic color.
In such a liquid crystal display, a color filter composed of pixels of the three primary colors (red, green, and blue) is used between a polarizer and a pixel electrode for displaying the hue. R, G, and B color filters are placed closely together, and a signal of a corresponding color is applied to each color filter to control a luminosity of the expressed color.
FIG. 1 represents color filter characteristics when white light is irradiated to the conventional R, G, and B color filter. As shown in FIG. 1, the color is conventionally expressed using the color filter that has a spatial period (d) of a color, wherein the spatial period has a value not larger than at least a spatial recognition value of a naked eye and the difference of a resolution is one pixel size.
Also, a color field sequential method is a known method by which to obtain a good picture quality without using a color filter, as shown in FIG. 2.
Referring to FIG. 2, there is illustrated the color field sequential method which divides a display area. By eliminating a color filter on a panel, transmissivity of light is increased and a color of light is expressed during a time period, wherein the time period has a time value not larger than at least a time recognition value of a naked eye, and wherein the expressed color has a high spatial resolution.
To describe in detail, when dividing a single frame on the panel into three frames (a red frame, green frame, and a blue frame) and irradiating a back light for each frame for a duration of time during which the back light can be turned on, the time is calculated by subtracting a total data writing time Td and a liquid crystal response time Tlc. In this way, the back light has an increased brightness over a back light composed of one frame because each color is emitted during a time calculated by subtracting the total data writing time and a liquid crystal response time. Generally, when assuming that an entire frame time is the same, it is expressed as in the following formula 1.Tt=3Td+3Tlc+Tbl=3Tw+Tbl  Formula 1:
Herein, Tt represents an entire frame time, Td represents a time for writing data on an entire screen, Tlc represents the response time of a liquid crystal, Tbl represents a time during which a back light can be turned on, and Tw represents picture formation time, which is the sum of the response time of the liquid crystal and the time for writing data on the entire screen.
Generally, a liquid crystal display has 60 HZ frame ratio such that Tt=16.7 msec. Referring to the formula 1, the time during which the back light can be turned on is expressed as Tbl=Tt−3Tw. Due to this, the time during which the back light can be turned on is the time calculated by subtracting a value, which is the sum of the time, Td, for writing data and the liquid crystal response time, Tlc, multiplied by ‘3’ (the number of frames in the color field sequential method), from the entire frame time 16.7 msec.
The time, Td, for writing data, the sum, Tw, of the liquid crystal response time Tlc, and the number of frames are factors that affect the time during which the back light can be turned on. No significant increase in brightness is gained over what can be achieved conventionally because a limit is reached in trying to decrease the time, Td, for writing data when driving a liquid crystal display. Furthermore, the time, Tbl, during which the back light can be turned on, is reduced if the liquid crystal response time is increased so that the response time of the liquid crystal or the brightness of the liquid crystal display become inadequate.